System and method for bandwidth optimization in a network storage environment

ABSTRACT

According to one or more embodiments of the present invention, a network cache intercepts data requested by a client from a remote server interconnected with the cache through one or more wide area network (WAN) links (e.g., for Wide Area File Services, or “WAFS”). The network cache stores the data and sends the data to the client. The cache may then intercept a first write request for the data from the client to the remote server, and determine one or more portions of the data in the write request that changed from the data stored at the cache (e.g., according to one or more hashes created based on the data). The network cache then sends a second write request for only the changed portions of the data to the remote server.

RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 11/694,356, filed Mar. 30, 2007 by Paul Jardetzky et al.,entitled SYSTEM AND METHOD FOR BANDWIDTH OPTIMIZATION IN A NETWORKSTORAGE ENVIRONMENT, the contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates generally to data storage environmentsand, more specifically, to bandwidth optimization of data transmissionin a network storage environment.

BACKGROUND OF THE INVENTION

A storage system typically comprises one or more storage devices intowhich information may be entered, and from which information may beobtained, as desired. The is storage system includes an operating systemthat functionally organizes the system by, inter alia, invokingoperations in support of a storage service implemented by the system.The storage system may be implemented in accordance with a variety ofstorage architectures including, but not limited to, a network-attachedstorage environment, a storage area network, and a disk assemblydirectly attached to a client or host computer. The storage devices aretypically disk drives organized as a disk array, wherein the term “disk”commonly describes a self-contained rotating magnetic media storagedevice. The term disk in this context is synonymous with hard disk drive(HDD) or direct access storage device (DASD).

In particular, in accordance with a network storage environment(generally), such as a Wide Area File System (WAFS) (or distributed filesystem) environment, information/data may be exchanged between one ormore storage systems and one or more clients over a network ofcommunication links. In such an environment, the storage system may beembodied as a server adapted to remotely serve and forward the data tothe client. For example, the clients and servers may be separated by awide area network (WAN), such as the Internet. As those skilled in theart will understand, communication between client and server thereforeinvolves transmission of the data over the links, utilizing anassociated amount of bandwidth on those links.

Generally, network communication links for data transmission may beexpensive, as will be understood by those skilled in the art. Forinstance, certain monetary costs may be associated with installing linksand/or using links (e.g., using a service provider's installed links),such as based on an amount of data transmission (e.g.,band-width/throughput) over those links. Accordingly, network storageenvironments may employ one or more storage systems configured asnetwork caches located at or near the clients to reduce the costsassociated with data transmission. In particular, network caches,generally, may be used to “cache” (store) data locally to the client,such that when a client needs the data, the data need not traverse thenetwork from the remote server if the data is already stored at thecache. Various configurations for network caches may include“write-through” (data is always written from the client “through” thecache to the server) and “write-back” caches (data is written fromclient “back to” the cache, and when necessary or when more optimal,written through to the server). In a write-through cache, only readperformance is optimized, since each write operation or request from theclient still traverses the network to the server. In a write-back cache,read and write performance is optimized with possibly fewer read andwrite requests traversing the network.

While network caches may advantageously optimize (i.e., reduce) thefrequency of data transmissions, the actual transmission of data to theserver still requires the utilization of bandwidth through the network.As mentioned above, however, the cost of the actual transmission of datathrough the network may generally be expensive. On the other hand,general-purpose computational processing speeds (e.g., for centralprocessing units, CPUs) continue to increase and their prices decreasemuch more rapidly than do network connection speeds and prices. (Inother words, it may be less expensive to purchase faster processingresources than to pay for faster/larger network connections.) As aresult, it may thus be desirable to apply the relatively inexpensiveresources (e.g., computational resources) toward optimizing bandwidthutilization over networks, particularly, for example, to reduce theactual data transmissions over expensive networks.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art byproviding a technique for optimized network bandwidth utilization in anetwork storage environment. The novel technique optimizes networkbandwidth utilization in a network storage environment, particularlybetween a network cache and a remote server. By only transmitting thechanged portions of cached data, traffic sent between the cache andremote server may be substantially reduced. In particular, the noveltechnique may conserve potentially is expensive WAN link resources byutilizing relatively inexpensive computation resources.

According to one or more embodiments of the present invention, a networkcache intercepts data requested by a client from a remote serverinterconnected with the cache through one or more wide area network(WAN) links (e.g., for Wide Area File Services, or “WAFS”). The networkcache stores the data and sends/transmits the data to the client. Thecache may then intercept a first write request for the data from theclient to the remote server, and determine one or more portions of thedata in the write request that changed from the data stored at the cache(e.g., according to one or more hashes created based on the data). Thenetwork cache then sends/transmits a second write request for only thechanged portions of the data to the remote server.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which like reference numerals indicateidentical or functionally similar elements:

FIG. 1 is a schematic block diagram of an example network storage systemenvironment;

FIG. 2 is a schematic block diagram of an example cache;

FIG. 3 is a schematic block diagram of example data;

FIG. 4 is a schematic block diagram of an example set of hashes;

FIG. 5 is a schematic block diagram of an example table of storedhashes;

FIG. 6 is a schematic block diagram of an example comparison between twoexample sets of hashes;

FIG. 7 is a flowchart of example steps for optimizing bandwidthutilization in a network storage environment in accordance with thepresent invention; and

FIG. 8 is an example data exchange/handling sequence in accordance withthe flowchart of FIG. 7.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

In accordance with one or more embodiments of the present invention, atechnique is provided that optimizes network bandwidth utilization in anetwork storage environment, particularly between a network cache and aremote server. By only transmitting the changed portions of cached data,traffic sent between the cache and remote server may be substantiallyreduced. In particular, the novel technique may conserve potentiallyexpensive WAN link resources by utilizing relatively inexpensivecomputation resources.

A. Network Storage System Environment

FIG. 1 is a schematic block diagram of a network storage systemenvironment 100 that may be advantageously used with the presentinvention, e.g., a wide area file system (WAFS). The storage systemenvironment 100 comprises a storage system embodied as a server 125(e.g., having one or more storage devices to store data) interconnectedwith one or more clients 110 by a network 120. The server 125 may beconfigured to operate as part of a network file system (e.g., as anetwork “filer”), as will be understood by those skilled in the art, tostore and provide data (e.g., files) to the clients 110. Illustratively,the network 120 may be embodied as an Ethernet network, a synchronousoptical network (SONET), or Frame Relay network of communication links,or, in particular, a wide area network (WAN), e.g., the Internet.Disposed between the server 125 and clients 110, specifically, betweenthe clients and the network 120, may be a storage system configured as anetwork cache 200 that illustratively implements the bandwidthoptimization technique of the present invention.

In operation, the server 125 remotely services data access requests(e.g., read/write requests) issued by the clients 110 over the network120. Each client 110 may be a general-purpose computer configured toexecute applications and interact with the remote server 125 inaccordance with a client/server model of information delivery. That is,the client may request the services of the server, and the server mayreturn the results of the services requested by the client, byexchanging packets over the network 120. The clients may issue packetsincluding file-based access protocols, such as the Common Internet FileSystem (CIFS) protocol or Network File System (NFS) protocol, overTCP/IP when accessing information, such as data, in the form of datacontainers, such as files and directories. Alternatively, the client mayissue packets including block-based access protocols, such as the SmallComputer Systems Interface (SCSI) protocol encapsulated over TCP (iSCSI)and SCSI encapsulated over Fibre Channel (FCP), when accessinginformation in the form of data containers, such as blocks.

B. Network Cache System

FIG. 2 is a schematic block diagram of a network cache 200 that may beadvantageously used with the present invention, e.g., a caching filer.Illustratively, the network cache 200 is embodied as a computer, and, assuch, may comprise a plurality of network interfaces 210, one or moreprocessors 220, and a memory 240 interconnected by a system bus 250. Thenetwork interfaces 205 contain the mechanical, electrical, and signalingcircuitry for communicating data over wired/wireless links coupled tothe network (storage environment) 100. The network interfaces 210 may beconfigured to transmit and/or receive data using a variety of differentcommunication protocols, including, inter alia, TCP/IP, UDP, ATM,synchronous optical networks (SONET), wireless protocols, Frame Relay,Ethernet, Fiber Distributed Data Interface (FDDI), etc.

The memory 240 comprises a plurality of storage locations that areaddressable by the processor(s) 220 for storing software programs anddata structures associated with the embodiments described herein. Theprocessors 220 may comprise necessary elements or is logic adapted toexecute the software programs and manipulate the data structures, suchas a table of stored hashes 500 (described below). An operating system242, portions of which are typically resident in memory 240 and executedby the processor(s), functionally organizes the network cache 200 by,inter alia, invoking operations in support of software processes and/orservices executing on the cache. These software processes and/orservices may comprise caching services 241 as well as an example hashgeneration process 243 and comparison process 245, each as describedherein. It will be apparent to those skilled in the art that otherprocessor and memory means, including various computer-readable media,may be used to store and execute program instructions pertaining to theinventive techniques described herein.

Caching services 241 contain computer executable instructions executedby processor(s) 220 to perform functions related to caching, generally,as will be understood by those skilled in the art. For instance, asmentioned above, caching services 241 may store data in memory (locationnot explicitly shown) as received from the remote server 125, such thatwhen a client 110 requests the data, the data need not traverse thenetwork 120 from the server if the data is already stored at the cache.Illustratively, the network cache may be configured as either a“write-through” cache or a “write-back” cache, as will be understood bythose skilled in the art.

As noted above, while the use of a network cache 200 may advantageouslyoptimize (i.e., reduce) the frequency of data transmissions (read andwrite requests), the actual transmission of data to and from the server125 still requires the utilization of bandwidth through the network 120.For example, various client applications perform sequential writeoperations or requests of entire files where only a small percentage ofthe files has been changed. In such an example circumstance, it may beinefficient to transmit the unchanged percentage of the files across thenetwork 120.

C. Bandwidth Optimization for Network Storage Environments

According to one or more embodiments of the present invention, a networkcache intercepts data requested by a client from a remote serverinterconnected with the cache through one or more wide area network(WAN) links (e.g., for Wide Area File Services, is or “WAFS”). Thenetwork cache stores the data and sends/transmits the data to theclient. The cache may then intercept a first write request for the datafrom the client to the remote server, and determine one or more portionsof the data in the write request that changed from the data stored atthe cache (e.g., according to one or more hashes created based on thedata). The network cache then sends/transmits a second write request foronly the changed portions of the data to the remote server.

Operationally, a client (e.g., 110 a) may request a particular set ofdata (e.g., data and meta-data for a file) from a remote server 125,such as through a read request over network 120. The remote server 125receives the request, and may respond with the requested data to satisfythe request. (Alternatively, the read request may originate at thenetwork cache 200, as those skilled in the art will understand.)Illustratively, FIG. 3 is an example schematic diagram of data 300 thatmay be used in accordance with the present invention, e.g., returnedfrom the remote server 125. For instance, one or more portions 305 ofthe data may be partitioned according to one or more corresponding databoundaries 310 (e.g., portions “D0” through “D7”). For example, the data300 may be block-based data, such as where each portion 305 correspondsto a 4 kilobytes (KB) block of data (e.g., “4 KB block”). Alternatively,the portions 305 may be based on network packets sent over the networklinks. In other words, if network packets are configured to carry 1 KBof data, then the boundaries 310 may divide the data 300 into 1 KBportions.

The data 300 travels through network 120 (e.g., a WAN) from the remoteserver 125 toward the requesting client (e.g., client 110 a), and isintercepted at network cache 200 located proximate to (i.e., local to)the clients 110. For example, by being physically located along the pathof the data stream (i.e., receiving the data 300), the network cache 200may intercept (or “capture”) the data 300 by actively receiving the data300, which is intended to be received by the clients 110 (e.g., thus,the network cache intercepts the data). Those skilled in the art willappreciate that in this manner, the network cache 200 operates in aconventional network cache manner. Notably, according to one or moreembodiments of the present invention, the network cache 200 may beconfigured to selectively intercept data 300, such as particular typesof data, data at particular times of day, is or may be manuallyactivated/deactivated, etc.

Upon intercepting the data, the cache may store (cache) the data, aswill be understood by those skilled in the art, and send the stored datato the requesting client accordingly. In addition, the network cache 200(e.g., hash generation process 243) may create (compute) a first set ofhashes based on the intercepted data 300. Notably, the first set ofhashes may be created prior to sending the data 300 to the client 110 orafter sending the data to the client once the data is cached.Alternatively, the server 125 may compute the set of hashes 400 and maytransmit the set along with the data to the cache 200. In this manner,the network cache 200 may receive the first set of created hashes alongwith the intercepted data 300 to be stored at the cache. (Note also,that while has generation process 243 is illustratively shown as asoftware process, those skilled in the art will appreciate that hashgeneration process 243 may also be alternatively or additionallyembodied as hardware.)

FIG. 4 is an example schematic diagram of a set of hashes 400 that maybe used in accordance with the present invention, e.g., created for thedata 300. For instance, the network cache 200 may create a set of hashes400, where each hash 405 of the set corresponds to a data portion 305 ofFIG. 3 above (e.g., “H0” corresponds to “D0”, “H1” to “D1”, etc.).Illustratively, the hashes may be created (e.g., by the cache 200 orremote server 125) in accordance with a one-way hashing function thatoperates to create no “collisions” (i.e., where substantially no twohashes are alike). As will be understood by those skilled in the art,example hashing functions may be the known “MD5” (Message DigestAlgorithm 5) or “SHA1” (Secure Hash Algorithm 1) encryption functions,as well as other suitable hashing functions not specifically notedherein.

As noted, the boundaries of the hashes 405 correspond to the databoundaries 310. (While the data boundaries 310 are shown above withreference to FIG. 3, the data 300 need not be divided into portionsitself, e.g., an 8 KB file may have no boundaries 310, but the hashcomputation configuration may divide the data into smaller portions uponwhich a hash is created, e.g., eight 1 KB portions.) That is, the hashes405 each correspond to a data portion 305 that is defined by boundaries310, which may correspond to a particular block size (e.g., 4 KBblocks), network packet size, some combination thereof, or otherbeneficial configuration not specifically mentioned herein but will beunderstood by those skilled in the art. In particular, the granularityof the hashes 405 may be adjusted (e.g., dynamically based on changingblock/packet sizes) or manually (e.g., by a system administrator) toefficiently create and use the hashes as described herein. In otherwords, as will be appreciated by those skilled in the art, hashescorresponding to smaller portions may result in greater fine-tuning ofdifference detection (described below); however, there is a tradeoffbetween fine-tuning and the cost/time of computation/processing of thegreater number of smaller hashes.

Illustratively, the sets of hashes 400 created for the intercepted data300 from the remote server 125 may also be stored at the network cache200, e.g., with the corresponding cached data. FIG. 5 illustrates anexample table of stored hashes 500 in accordance with one or moreembodiments described herein. The table of stored hashes 500 isillustratively stored in memory 240 and may include one or more entries520, each comprising a plurality of fields, such as a data identifier(ID) field 505 and an associated/corresponding hash set field 510. Thetable of stored hashes 500 is illustratively maintained and managed byhash generation process 243 and/or comparison process 245. To that end,the table of stored hashes 500 maintains sets of hashes 400 (e.g., thefirst set of hashes) corresponding to particular instances ofintercepted data 300 in accordance with the techniques as describedherein. For instance, the network cache 200 may receive/intercept dataidentified as “Data A” through “Data N” (e.g., identified by a filename/handle, path name, or other data/meta-data as will be understood bythose skilled in the art) and stored in data ID field 505, and may storecorrespondingly created sets of hashes “Hash Set A” through “Hash Set N”in the hash set field 510 of the table 500 (that is, storing sets ofhashes 400 in hash set field 510).

As mentioned above, the network cache 200 forwards the intercepted datato the requesting client 110 a. The client may process the data, as willbe understood by those skilled in the art (e.g., accesses, reads, opens,modifies, etc.), and (if the data does not correspond to a read-onlyfile) may send a first write request for the data toward the remoteserver 125 (or, if configured to be so aware, directly to the cache200). The network cache 200 may then intercept (or receive) the firstwrite request, and create a second set of hashes 400 of the data 300 inthe write request using whichever hash function that was used to createthe first set of hashes 400 above. For example, if MD5 was used on thedata at boundaries corresponding to 4 KB blocks to create the first setof hashes, then the second set of hashes is created using MD5 on 4 KBblocks.

Once the second set of hashes is created, the network cache 200 (e.g.,comparison process 245) may compare the first and second sets of hashes400 to determine whether there are any differences. For example, FIG. 6illustrates a schematic diagram of a comparison operation between twoexample sets of hashes 400 in accordance with the present invention. Thefirst set of hashes 400 a created from the intercepted data 300 from theremote server (the stored/cached data) may have hashes H0-H7 thatcorrespond respectively to “L, M, N, O, P, Q, R, S”. (Those skilled inthe art will understand that the use of simple letters is merely forillustrative purposes, and that actual hashes are generally far morecomplex.) The second set of hashes 400 b created from the received datain the first write request from the client may have hashes H0-H7 thatcorrespond respectively to “L, M, N, T, P, Q, U, V”. If the first andsecond sets of hashes 400 match, there is no need to transmit thatcorresponding portion of data 305 over the network since the portion hasnot changed (e.g., portions D0-D2, and D4-D5). Those hashes that aredifferent upon comparison, however, denote a change in thosecorresponding portions of data, and such portions are sent to the remoteserver 125 over the network 120 accordingly (e.g., portions D3 andD6-D7).

Upon completion of the comparison, in accordance with the presentinvention, the network cache 200 may generate and send a second writerequest (e.g., 610) to the remote server 125 (on behalf of the client110 a) that contains only the data portions that have changed (e.g., D3,D6, and D7). The remote server 125 may be configured to receive such“partial” write requests, and updates the copy of the data 300 stored atthe server with the changed data (e.g., updates the data portions D3 andD6-D7). In this manner, transmission of the data across the network 120is reduced to those portions that have changed (to those whose newhashes do not match the stored hashes). As the remainder of the data hasnot changed (new hashes match the stored hashes), the unchanged datadoes not need to be re-written (i.e., transmitted) to the server.Accordingly, network traffic is reduced, and bandwidth is efficientlyoptimized.

As noted, the data portion size may be adjusted (or pre-configured) toallow for an efficient use and application of resources. For instance,it may be appreciated that a single hash for the entire data 300 may beconsidered inefficient, as a change of a single bit (e.g., a date-stamp)may result in all of the data being transmitted to the server (i.e., thechanged portion). Conversely, a hash created for each bit of the datamay result in an extreme computational burden, and thus may also beconsidered inefficient.

Moreover, for write-back caches, the techniques described herein may beapplied at the network cache 200 prior to sending the second writerequest to the remote server 125, but not necessarily each time a firstwrite request for the data is received from the client 110 a. Inparticular, because a write-back cache typically only sends data overthe network 120 when possible/desired, only the data to be actually sentto the remote server needs to be compared with the original stored dataintercepted from the remote server (i.e., what the remote server shouldcurrently contain for the data). Write-through caches, on the otherhand, typically send the data to the remote server upon each writerequest from the client, and as such, would benefit from performing thecomparison for each request, accordingly.

FIG. 7 is a flowchart detailing the steps of a procedure 700 foroptimizing bandwidth utilization in a network storage environment inaccordance with an illustrative embodiment of the present invention.Also, FIG. 8 illustrates an example data exchange/handling sequence 800in accordance with the steps of FIG. 7. The procedure 700 (andillustrative sequence 800) begins in step 705 and continues to step 710where a client (e.g., 110 a) sends a read request for data (e.g., DataA) to a remote server 125 interconnected with the client through one ormore network (e.g., WAN) links 120. In response, the server 125 sendsthe requested data (Data A) toward the client 110 a in step 715.

In step 720, the network cache 200 intercepts the requested data (andcaches it), and hash generation process 243 correspondingly creates afirst set (e.g., 400 a) of one or more hashes from the data in step 725,as described above. The cache 200 then stores the data and hashes (e.g.,in stored hashes table 500) in step 730, and sends the data (Data A) tothe client 110 a as originally intended in step 735. (Notably, while thesteps shown herein illustrate creating the hash prior to sending thedata to the client, embodiments of the present invention mayalternatively send the data to the client once the data is cached, andmay perform the hashing operations afterward.) In step 740, the clientmay receive and process the data, and may subsequently send theprocessed data toward the remote server 125 in step 745, e.g., in afirst write request.

In step 750, the network cache 200 intercepts the processed data (thefirst write request), and creates a second set (400 b) of one or morehashes from the processed data in step 755 (e.g., hash generationprocess 243). With both the first and second sets of hashes for the data(Data A) (or, as mentioned above, with both sets of data), thecomparison process 245 of the cache may determine, in step 760, one ormore portions 305 of the data in the write request changed from the datastored at the cache. Accordingly, as described above, the network cache200 may send only the changed portions 605 of the data to the remoteserver 125 (e.g., a second write request, 610) in step 765, thuspotentially reducing (optimizing) network bandwidth utilization acrossnetwork 120. The procedure 700 then ends in step 770.

Advantageously, the novel technique optimizes network bandwidthutilization in a network storage environment, particularly between anetwork cache and a remote server. By only transmitting the changedportions of cached data, traffic sent between the cache and remoteserver may be substantially reduced. In particular, the novel techniquemay conserve potentially expensive WAN link resources by utilizingrelatively inexpensive computation resources.

In other words, through the techniques described herein, such asutilizing block/packet-based hashes and a differencing engine (comparingprocess 245), the network cache 200 may advantageously decide if andwhen to transmit a particular portion of data across the network.Accordingly, the present invention effectively optimizes bandwidthutilization for network storage environments, particularly for networkcaches 200, by avoiding transmission of “duplicate data” (data notchanged and already stored on the cache and remote server) for a writerequest. Notably, those skilled in the art will appreciate that whiledata de-duplication technology is available to avoid storage ofduplicate data, the techniques described herein may be particularly usedto reduce transmission of unnecessary (duplicate) data across a network.

While there have been shown and described illustrative embodiments thatoptimize network bandwidth utilization in a network storage environment,it is to be understood that various other adaptations and modificationsmay be made within the spirit and scope of the present invention. Forexample, the embodiments have been shown and described herein showing anetwork cache 200 that is separate from the clients 110 (e.g.,separately connected via one or more LAN links). However, theembodiments of the invention in their broader sense are not so limited,and may, in fact, be applicable to caches that are co-located within theclients 110. Further, while the above description utilizes WAN links forthe network communication links, it should be noted that the networkstorage environment may utilize any network links generally (e.g., LANlinks, wireless links, etc.) that may be used to interconnect separatenodes/devices, e.g., clients, caches, servers, etc. Also, while theabove description utilizes (e.g., creates and compares) hashescorresponding to the data to determine differences, the stored data andthe data of the write request may be directly compared without a needfor hashes. Those skilled in the art will understand that it many caseshashes may be substantially smaller in size than the actual data (e.g.,a 128-bit MD5 hash that corresponds to a 4K block of data), and thus maybe more efficiently compared.

Furthermore, while this description has been written in terms ofreducing data sent over communication links, the principles of thepresent invention may be utilized to provide bandwidth optimizationwithin a single node/device. In such an alternate embodiment, theabove-described caching technique may be used to minimize the amount ofbandwidth utilized in transmitting data within the device (e.g., on asystem bus 250), should such a configuration be advantageous.

The foregoing description has been directed to specific embodiments ofthis invention. It will be apparent, however, that other variations andmodifications may be made to the described embodiments, with theattainment of some or all of their advantages. For instance, it isexpressly contemplated that the teachings of this invention can beimplemented as software, including a computer-readable medium havingprogram instructions executing on a computer, hardware, firmware, or acombination thereof. Accordingly this description is to be taken only byway of example and not to otherwise limit the scope of the invention.Therefore, it is the object of the appended claims to cover all suchvariations and modifications as come within the true spirit and scope ofthe invention.

1. A method, comprising: intercepting, at a cache having a processor,first data requested by a client from a server; in response tointercepting the first data at the cache, storing the first data at thecache; intercepting, at the cache, a first write request for second datafrom the client to the server; determining, by the cache, one or moreportions of the second data that differ from the first data; and sendinga second write request for the one or more portions of the first datathat differ from the first data to the server.
 2. The method of claim 1further comprising creating a first set of hashes of the first data. 3.The method of claim 1 further comprises creating a second set of hashesof the second data.
 4. The method of claim 1 wherein the cache, theserver and the client operate in accordance with Wide Area File Services(WAFS).
 5. A system, comprising: a remote server configured to senddata; a network cache having a processor and operatively interconnectedbetween the remote server and a client through one or more wide areanetwork (WAN) links, the network cache configured to intercept the datasent from the remote server and requested by the client, store the data,and send the requested data to the client; and the client configured toreceive the requested data from the network cache, process the data, andsend a first write request for the processed data to the remote server;wherein the network cache is further configured to intercept the firstwrite request and further configured to send a second write request forportions of the processed data that changed to the remote server.,wherein only the portions of the processed data that changed between thestored data and the processed data are included in the second writerequest.